1. Field of the Invention
This invention relates to medical instrumentation and, more specifically, to such instrumentation applied in the field of cardiac surgery and peripheral vascular surgery.
2. Prior Art
Arterial reconstruction utilizing an autologous saphenous vein is widely used in the field of peripheral vascular surgery in the lower extremities and so has become well established as the customary graft source for aorto-coronary bypass graft surgery.
In peripheral vascular surgery in-situ bypass grafting has become more and more the operation of choice for bypassing the infrageniculate arteries and re-establishing arterial blood flow. The autogenous saphenous vein is historically similar to an artery and is the standard to which all other grafts are compared.
The earliest experiences with venous autogenous grafts, although experimental at that time, were gained by Gluck in 1894, followed by Exner and Hopfner in 1903. In the United States, Julian, et al., Lord and Stone, Dale, et al., and Linton and Darling pioneered the wide use of an autologous vein in femoral-popliteal arterial reconstructive procedures. The concept of using the saphenous vein, in-situ, is attributed to Karl Hall, in 1959, who suggested that the saphenous vein bypass might improve if the vein were left in place and the valves were rendered incompetent. He was the first to successfully report the use of the in-situ procedure as an arterial bypass, in 1962.
Further, the technique of in-situ bypass grafting was augmented by Leather and Karmody who used valve strippers to disrupt the grafted vein valves.
With the increasing experience worldwide, it was apparent that the crux of the in-situ vein graft was the method of removal of the valvular obstruction to distal arterial flow.
To achieve the in-situ disruption of the valves, various techniques have been used:
1. Incision of the valves by miniature scissors inserted through a venotomy proximal to the respective valve site.
2. Thin incising vein-strippers passed through the vein in the distal to the proximal direction.
3. Bullet-shaped metal strippers introduced in anterograde or retrograde directions, employing incising parts in different shapes.
4. Long, thin-shaped valvulotomes with curved, hook-like incising tips which incise the valve leaflets upon pulling the device back through the valve.
5. Double cylinder strippers having incising parts incising the valves when such parts are pulled in a reverse direction.
6. Thin incision fingers extending from the open distal end of a catheter that is being pulled from the proximal part of the vein towards its distal portion by a pulling instrument that has been secured to the catheter after being introduced through the distal part of the vein.
In cardiac surgery, autologous saphenous vein grafts have been widely used since 1967 in aorto-coronary bypass grafting procedures for symptomatic coronary artery disease (CAD) treatment.
Autogenous reversed saphenous vein grafting has become routine for aorto-coronary bypass surgery.
With this method the saphenous vein valves are left intact and the vein is reversed. The distal portion of the grafted vein (which becomes proximal in the graft) is usually larger in diameter than the replaced coronary artery, resulting in reduced blood flow velocity in the vein graft compared with that in the coronary artery. These grafts provide an early patency rate of 98%; a routine elective mortality rate of approximately 1%, and a myocardial infarction rate of approximately 3%. The patency rate of coronary vein grafts is approximately 85% by the end of the first year postoperatively and the attrition rate continues approximately 2% per year for the next 4-5 years. Progressive stenosis continues, and the patency rate of coronary vein grafts at 3 years postoperatively is approximately 70% and approximately 60% at 5 years postoperatively.
At 10 years postoperative, atherosclerosis becomes the major cause of coronary vein graft failure. The vein graft occlusion rate doubles between 5 and 10 years, postoperatively.
Performance of coronary reversed saphenous vein grafts relates, among other factors, to the intact valves, which are implicated in graft failure. Studies suggest that valves do not open fully during reversd blood flow and cause a decrease in the graft blood flow rate at specific obstruction-related points. The undisrupted valves, non-collapsed against the wall of the grafted vein, may cause them to stay in the main blood stream and become a site of turbulence to laminar flow and an origin for thrombus formation under the cusps. This is especially true with the decreased blood flow rate in large diameter vein grafts and with poor run-off.
Thrombosis may lead, in these cases, to myocardial infarction or, later, to increased stenosis and occlusion. Laminar flow at the venous valves causes a reaction of the vein grafts similar to a spasm, suggesting that the valves may be a predisposed to an increased stenosis rate and a rapid occlusion rate of the vein grafts.
Additional experience evidenced that when more than one valve site was present in the body of the saphenous vein graft, occlusion, thrombus formation or accelerated progressive atherosclerosis seemed to occur in anatomic correlation to these valve. Good flow velocity is essential to the patency and integrity of coronary vein bypass grafts, while flow disturbance and decreased blood flow velocity are important influencing factors affecting their integrity as well as short term and long term patency.
Bisection of vein valves significantly increases the blood flow rate through the vein grafts.
Prior art devices, while rendering the saphenous veins relatively incompetent, did not remove the valves, with the result that complications such as stenosis, occlusion and thrombus formation, as previously recited, occurred. In cardiac surgery the protocol or coronary reversed vein grafts is subject to review and reversion if improved instrumentation becomes available, and is proven to be effective to enhance potency rate and integrity.
Therefore, it is an object of this invention to provide a medical instrument that will overcome the general problems recited hereinbefore.
It is a further object of this invention to provide an easy to operate cutting catheter that will cut and remove, effectively, the valves in the saphenous veins used as grafts for bypass peripheral surgery and aorto-coronary bypass surgery.